The novel follows a young boy, Capricorn "Cap" Anderson raised in an isolated hippie commune who is sent to live with foster parents and attend public school following his grandmother's accident.

Capricorn Anderson, nicknamed "Cap," and his grandmother, Rain, are hippies living on Garland Farm, a far-removed commune with no telephone service.

Capricorn is sent to live with social worker Flora Donnelly, a former resident of Garland Farm, after she realizes that she herself is the best person to look after Cap.

Flora decides to enroll Cap in Claverage Middle School (dubbed C-Average by the student body) as an eighth grader while Rain recovers.

On his first day, he meets eighth-grade bully and jock Zachary "Zach" Powers, who singles him out for the school's biggest prank: electing the most unpopular student as the Eighth Grade President and besetting the victim with impossible demands, causing them to break down.

Flora, realizing that Cap's obliviousness to social life and bullying protects him from the brunt of the abuse, reluctantly keeps silent.

Despite disapproval from adults and the authorities, Cap gains newfound popularity at C Average, causing Zach's plan to ultimately backfire.

He is picked up by Sophie, who has passed her driving exam and feels remorseful of her scornful behavior towards him, having realized who her belated gift came from.

She tells him that she sold Garland for seventeen million dollars, and that she has bought a condo for the two to live in and has taken inspiration from Cap's actions with the school's money to create a charitable foundation.